Tail pipe

ABSTRACT

Provided is a tail pipe in which a silencing effect at a discharge port is obtained. One aspect of the present disclosure is a tail pipe including: an inner tube including a discharge port configured such that an exhaust gas is discharged therefrom; an outer tube arranged so as to form a space between the outer tube and the inner tube by surrounding an outer peripheral surface of the inner tube, an upstream end of the outer tube in a flow direction of the exhaust gas being closed; and at least one communication hole allowing communication between an interior of the inner tube and the space.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of Japanese Patent Application No.2019-018056 filed on Feb. 4, 2019 with the Japan Patent Office, theentire disclosure of which is incorporated herein by reference.

BACKGROUND

The present disclosure relates to a tail pipe.

In an exhaust system of an internal combustion engine, a tail pipe isknown that is enlarged in diameter toward an exhaust port and that hasgrooves spirally formed of concavities and convexities on a peripheralwall for the purpose of increasing exhaust efficiency (see JapaneseUtility Model Registration No. 3021165).

In this tail pipe, exhaust flow is twisted by the grooves, and a flowvelocity of the exhaust flow is thereby increased. This results inimproving the exhaust efficiency.

SUMMARY

In tail pipes of exhaust systems, noise is generated by air flowproduced when an exhaust gas is discharged into the atmosphere. In theabove-described tail pipe, the exhaust efficiency is improved by theabove-described action, but noise reduction effect cannot be expected.

In one aspect of the present disclosure, it is desirable to provide atail pipe in which a silencing effect at a discharge port is obtained.

One aspect of the present disclosure is a tail pipe comprising: an innertube comprising a discharge port configured such that an exhaust gas isdischarged therefrom; an outer tube arranged so as to form a spacebetween the outer tube and the inner tube by surrounding an outerperipheral surface of the inner tube, an upstream end of the outer tubein a flow direction of the exhaust gas being closed; and at least onecommunication hole allowing communication between an interior of theinner tube and the space.

Such a configuration allows the space inside the outer tubecommunicating with the interior of the inner tube to function as aresonance chamber. This results in obtaining a silencing effect at thedischarge port due to a resonance effect in the space.

In one aspect of the present disclosure, the inner tube may comprise anenlarged diameter portion enlarged in diameter toward the dischargeport. In such a configuration, a flow velocity of the exhaust gas isreduced by the enlarged diameter portion. This facilitates rapid anduniform mixture of the exhaust gas into the atmosphere, resulting inreducing air flow noise.

In one aspect of the present disclosure, the enlarged diameter portionmay comprise a gently enlarged portion having a first taper angle, and asharply enlarged portion having a second taper angle larger than thefirst taper angle. In such a configuration, the flow velocity of theexhaust gas is changed in a circumferential direction of the tail pipeby the sharply enlarged portion and the gently enlarged portion.Specifically, the exhaust gas discharged along the gently enlargedportion is likely to spread more outward in a radial direction than theexhaust gas discharged along the sharply enlarged portion. Thus, flowvelocity distribution of the exhaust gas discharged from the dischargeport exhibits an elliptical shape with a portion along the gentlyenlarged portion as a major axis. Consequently, an area where theexhaust gas contacts the atmosphere is increased, thus facilitatingrapid and uniform mixture of the exhaust gas into the atmosphere. Thisresults in facilitating reduction of air flow noise.

In one aspect of the present disclosure, the at least one communicationhole may be arranged in the sharply enlarged portion. Such aconfiguration makes it unlikely for the exhaust gas to hit an edgeportion of the at least one communication hole, thus reducing separationof the exhaust gas from an inner circumferential surface of the innertube. Consequently, turbulent flow of the exhaust gas is unlikely to begenerated on the inner circumferential surface of the inner tube,resulting in reducing air flow noise (i.e., whistling noise) to begenerated when the exhaust gas passes through the at least onecommunication hole.

In one aspect of the present disclosure, the at least one communicationhole may be shaped such that a width thereof in a circumferentialdirection of the inner tube changes along the flow direction of theexhaust gas. Such a configuration reduces an area where the exhaust gashits the edge portion of the at least one communication hole, ascompared with a communication hole with unchanged width in thecircumferential direction. As a result, separation of the exhaust gasfrom the inner circumferential surface of the inner tube is reduced,thus inhibiting generation of air flow noise at the at least onecommunication hole.

In one aspect of the present disclosure, a downstream end of the outertube in the flow direction of the exhaust gas may be closed. Such aconfiguration allows the space inside the outer tube to be an enclosedspace, thus forming a Helmholtz resonator. This results in improving thesilencing effect at the discharge port.

In one aspect of the present disclosure, a downstream end of the outertube in the flow direction of the exhaust gas may be open so as to allowcommunication between the space and an outside of the outer tube. Insuch a configuration, the exhaust gas with a higher velocity dischargedfrom the inner tube is covered by the exhaust gas with a lower velocitydischarged from the outer tube, and the atmosphere exists furthertherearound. This causes gradual decrease in the flow velocity of theexhaust gas flowing on the outer side, thus lowering likelihood ofgeneration of turbulent flow. As a result, generation of air flow noisedue to the turbulent flow can be reduced.

BRIEF DESCRIPTION OF THE DRAWINGS

Example embodiments of the present disclosure will be described belowwith reference to the accompanying drawings, in which:

FIG. 1A is a schematic plan view of a tail pipe according to anembodiment, and FIG. 1B is a schematic side view of the tail pipe ofFIG. 1A;

FIG. 2 is a schematic partial sectional view taken along line II-II ofFIG. 1A;

FIG. 3 is a schematic diagram showing one example of a shape of acommunication hole;

FIG. 4 is a schematic partial sectional view of a tail pipe according toan embodiment different from that of FIG. 1A;

FIG. 5 is a schematic plan view of a tail pipe according to anembodiment different from those of FIGS. 1A and 4; and

FIG. 6 is a schematic plan view of a tail pipe according to anembodiment different from those of FIGS. 1A, 4, and 5.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS 1. First Embodiment 1-1.Configuration

A tail pipe 1 shown in FIGS. 1A and 1B is provided to an end of anexhaust gas flow path of an internal combustion engine. The tail pipe 1discharges, into the atmosphere, an exhaust gas discharged from theinternal combustion engine. The tail pipe 1 comprises an inner tube 2,an outer tube 3, and communication holes 4A and 4B.

The internal combustion engine to which the tail pipe 1 is applied isnot limited in particular. Examples of such an internal combustionengine may include those used for drive or power generation in transportequipment, such as an automobile, a railroad car, a ship, andconstruction equipment, power generation facilities, and so on.

<Inner Tube>

The inner tube 2 is a metal pipe through which an exhaust gas G passes.The inner tube 2 comprises a supply port 21 through which the exhaustgas G is supplied, a discharge port 22 through which the exhaust gas Gpassed through the inner tube 2 is discharged, and an enlarged diameterportion 23 enlarged in diameter toward the discharge port 22.

The enlarged diameter portion 23 comprises a gently enlarged portion 24having a first taper angle, and two sharply enlarged portions 25A and25B each having a second taper angle larger than the first taper angle.The enlarged diameter portion 23 may comprise one sharply enlargedportion, or three or more sharply enlarged portions. The first taperangle is an angle between a surface of the gently enlarged portion 24and a central axis of the inner tube 2. The second taper angle is anangle between a surface of each of the sharply enlarged portions 25A and25B and the central axis of the inner tube 2. The first taper angle isan acute angle. The second taper angle is an acute angle or a rightangle, and is preferably an acute angle.

The gently enlarged portion 24 is a portion enlarged in diameter at theconstant first taper angle in a region covered by the outer tube 3 to bedescribed later. The gently enlarged portion 24 may have a shapegradually increased in a degree of curve toward the discharge port 22,namely a flare shape. The gently enlarged portion 24 is provided, in acircumferential direction of the inner tube 2, throughout a regionexcept where the sharply enlarged portions 25A and 25B and straightportions 26A and 26B to be described later are formed.

The sharply enlarged portions 25A and 25B are each arranged in a part ofthe inner tube 2 in the circumferential direction thereof. The sharplyenlarged portions 25A and 25B do not overlap with the gently enlargedportion 24 when viewed along an axial direction of the inner tube 2. Inother words, the gently enlarged portion 24 is not formed upstream anddownstream of the sharply enlarged portions 25A and 25B.

In the present embodiment, the sharply enlarged portions 25A and 25B areeach arranged in a position overlapping with the gently enlarged portion24 when viewed along the circumferential direction of the inner tube 2.Further, the sharply enlarged portions 25A and 25B are each arrangedsuch that an upstream end thereof (i.e., an end where enlargement indiameter starts) coincides in position with an upstream end of thegently enlarged portion 24 in the axial direction of the inner tube 2.

The sharply enlarged portions 25A and 25B each comprise, on a downstreamside thereof, the straight portions 26A and 26B, respectively, having aconstant inside diameter. A width of each of the straight portions 26Aand 26B in the circumferential direction of the inner tube 2 becomesgradually smaller toward the discharge port 22. However, the width ofeach of the straight portions 26A and 26B in the circumferentialdirection of the inner tube 2 may be constant.

In the present embodiment, the sharply enlarged portions 25A and 25B arearranged in positions opposite each other in a radial direction of theinner tube 2 (i.e., positions spaced 180° apart in the circumferentialdirection of the inner tube 2). However, the sharply enlarged portions25A and 25B do not necessarily have to be arranged in such relativepositions.

<Outer Tube>

The outer tube 3 is a metal pipe arranged outside the inner tube 2 so asto surround an outer peripheral surface of the inner tube 2.

The inside diameter of the outer tube 3 excluding an upstream end 31 maybe more than or equal to 1.15 times and less than or equal to 1.5 timeslarger than the outside diameter of the inner tube 2 excluding theenlarged diameter portion 23 (i.e., than the outside diameter of aportion having a constant outside diameter).

As shown in FIG. 2, the outer tube 3 is arranged so as to form a space Sbetween the outer tube 3 and the inner tube 2 by surrounding the outerperipheral surface of the inner tube 2. In the outer tube 3, theupstream end 31 and a downstream end 32 in a flow direction of theexhaust gas G are both closed.

Specifically, the upstream end 31 of the outer tube 3 is reduced indiameter toward an outside thereof in an axial direction. The upstreamend 31 is fixed to a portion of the inner tube 2 located upstream of theenlarged diameter portion 23, circumferentially throughout by welding,for example.

The downstream end 32 of the outer tube 3 is fixed to downstream ends ofthe gently enlarged portion 24 and the straight portions 26A and 26B ofthe inner tube 2 (i.e., to ends forming the discharge port 22),circumferentially throughout by welding, for example. The outer tube 3contacts outer peripheral surfaces of the straight portions 26A and 26Bof the inner tube 2. The outer tube 3 excluding the upstream end 31 hasa constant diameter.

A shape of a section of the outer tube 3 perpendicular to an axialdirection thereof does not have to be a perfect circle. In the presentembodiment, an opening of the outer tube 3 at the downstream end 32coincides in position with the discharge port 22 of the inner tube 2 inthe axial direction of the inner tube 2. However, the opening of theouter tube 3 at the downstream end 32 may be located more outside in theaxial direction of the inner tube 2 than the discharge port 22 of theinner tube 2. In other words, the outer tube 3 may protrude outside ofthe inner tube 2 in the axial direction thereof.

From the viewpoint of design, the inner tube 2 at the discharge port 22and the outer tube 3 at the downstream end 32 may be inclined withrespect to the radial direction of the inner tube 2. In other words, thedownstream ends of the inner tube 2 and the outer tube 3 may each have acut surface inclined with respect to a plane perpendicular to thecentral axis of the inner tube 2.

<Communication Hole>

The communication holes 4A and 4B each allow communication between aninterior of the inner tube 2 and the space S. In the present embodiment,the sharply enlarged portions 25A and 25B each contain a single hole,namely the communication holes 4A and 4B, respectively.

However, the sharply enlarged portions 25A and 25B may each contain twoor more communication holes as long as a silencing effect for a targetfrequency is obtained.

In the present embodiment, the communication holes 4A and 4B are notarranged in any portion of the inner tube 2 other than the sharplyenlarged portions 25A and 25B.

Shapes of the communication holes 4A and 4B each may be an ellipse, apolygon, or the like, instead of the shown perfect circle. Further, thecommunication holes 4A and 4B may be shaped such that a width thereof inthe circumferential direction of the inner tube 2 changes along the flowdirection of the exhaust gas G. This reduces an area where the exhaustgas G hits an edge portion of each of the communication holes 4A and 4B,as compared with the communication holes 4A and 4B with unchanged widthin the circumferential direction. As a result, separation of the exhaustgas G from an inner circumferential surface of the inner tube 2 isreduced, thus inhibiting generation of air flow noise at thecommunication holes 4A and 4B. Examples of such a shape may include ateardrop shape shown in FIG. 3, as well as a rhombus and an ellipse.

A flange or a louver protruding inward or outward of the inner tube 2may be provided around the communication holes 4A and 4B. In otherwords, the communication holes 4A and 4B may be drilled by processingsuch as burring, and cutting to raise. Sizes of the communication holes4A and 4B may be designed as appropriate.

1-2. Actions

In the tail pipe 1, the space S communicating with the interior of theinner tube 2 through the communication holes 4A and 4B forms a resonancechamber in the vicinity of the discharge port 22 of the inner tube 2.This results in obtaining a silencing effect at the discharge port 22.

Further, a flow velocity of the exhaust gas G is reduced by the enlargeddiameter portion 23, and flow layers of the exhaust gas G havingdifferent flow velocities in the circumferential direction of the innertube 2 are formed by the gently enlarged portion 24 and the sharplyenlarged portions 25A and 25B.

These flow layers allow the exhaust gas G discharged from the dischargeport 22 into the atmosphere to be assimilated and mixed into theatmosphere relatively rapidly. Thus, generation of turbulent flow and/orvortex is inhibited at the discharge port 22.

1-3. Effects

The embodiment detailed above produces the following effects.

(1a) The space S inside the outer tube 3, communicating with theinterior of the inner tube 2, functions as the resonance chamber. Thisresults in obtaining the silencing effect at the discharge port 22 dueto a resonance effect in the space S.

(1b) The flow velocity of the exhaust gas G is reduced by the enlargeddiameter portion 23 provided to the inner tube 2. This facilitates rapidand uniform mixture of the exhaust gas G into the atmosphere, resultingin reducing air flow noise.

(1c) The flow velocity of the exhaust gas G is changed in acircumferential direction of the tail pipe 1 by the sharply enlargedportions 25A and 25B and the gently enlarged portion 24. Specifically,the exhaust gas G discharged along the gently enlarged portion 24 islikely to spread more outward in the radial direction than the exhaustgas G discharged along the sharply enlarged portions 25A and 25B. Thus,flow velocity distribution of the exhaust gas G discharged from thedischarge port 22 exhibits an elliptical shape with a portion along thegently enlarged portion 24 as a major axis. Consequently, an area wherethe exhaust gas G contacts the atmosphere is increased, thusfacilitating rapid and uniform mixture of the exhaust gas G into theatmosphere. This results in facilitating reduction of air flow noise.

(1d) The communication holes 4A and 4B are arranged in the sharplyenlarged portions 25A and 25B, respectively. This makes it unlikely forthe exhaust gas G to hit the edge portion of each of the communicationholes 4A and 4B, thus reducing separation of the exhaust gas G from theinner circumferential surface of the inner tube 2. Consequently,turbulent flow of the exhaust gas G is unlikely to be generated on theinner circumferential surface of the inner tube 2, resulting in reducingair flow noise (i.e., whistling noise) to be generated when the exhaustgas G passes through the communication holes 4A and 4B.

(1e) The downstream end 32 of the outer tube 3 is closed to therebyallow the space S inside the outer tube 3 to be an enclosed space, thusforming a Helmholtz resonator. This results in improving the silencingeffect at the discharge port 22.

2. Second Embodiment 2-1. Configuration

A tail pipe 1A shown in FIG. 4 comprises the inner tube 2, an outer tube3A, and the communication holes 4A and 4B. The inner tube 2 and thecommunication holes 4A and 4B are the same as those of the tail pipe 1of FIG. 1.

The outer tube 3A is the same as the outer tube 3 of the tail pipe 1 ofFIG. 1 except for a configuration of a downstream end 32A. In the outertube 3A, an upstream end 31A in the flow direction of the exhaust gas Gis closed, whereas the downstream end 32A is not closed but open.

Specifically, the downstream end 32A of the outer tube 3A has an opening33A allowing communication between the space S and the outside of theouter tube 3A. Thus, the space S of the present embodiment is notenclosed but open to the atmosphere. The outer tube 3A except for theupstream end 31A is spaced apart from the inner tube 2.

In the present embodiment, the opening 33A of the outer tube 3A at thedownstream end 32A is located more outside in the axial direction of theinner tube 2 than the discharge port 22 of the inner tube 2. In otherwords, the outer tube 3A protrudes outside of the inner tube 2 in theaxial direction thereof. This causes the exhaust gas G discharged fromthe discharge port 22 to expand at the opening 33A, thus enablingfurther reduction of the velocity of the exhaust gas G discharged fromthe opening 33A. However, the opening 33A of the outer tube 3A maycoincide in position with the discharge port 22 of the inner tube 2 inthe axial direction of the inner tube 2.

The minimum distance D in the radial direction of the inner tube 2between the enlarged diameter portion 23 of the inner tube 2 and theouter tube 3A (i.e., a thickness of the space S at the discharge port22) is designed to have a size allowing the space S to function as theresonance chamber for the exhaust gas G.

2-2. Actions

In the tail pipe 1A, the exhaust gas G passes through the space S and isdischarged from the opening 33A of the outer tube 3A. Thus, flow layersof the exhaust gas G having different flow velocities in the radialdirection of the inner tube 2 are formed.

Further, in the tail pipe 1A, an outer-side flow of the exhaust gas Gdischarged from the opening 33A of the outer tube 3A reduces thevelocity of a central flow of the exhaust gas G discharged from thedischarge port 22 of the inner tube 2.

2-3. Effects

The embodiment detailed above produces the following effect.

(2a) The exhaust gas G with a higher velocity discharged from the innertube 2 is covered by the exhaust gas G with a lower velocity dischargedfrom the outer tube 3, and the atmosphere exists further therearound.This causes gradual decrease in the flow velocity of the exhaust gas Gflowing on the outer side, thus lowering likelihood of generation ofturbulent flow. As a result, generation of air flow noise due to theturbulent flow can be reduced.

3. Other Embodiments

Although the embodiments of the present disclosure have been describedso far, the present disclosure is not limited to the above-describedembodiments, and can be practiced in various forms.

(3a) In the tail pipes of the above-described embodiments, the sharplyenlarged portions 25A and 25B do not necessarily have to overlap withthe gently enlarged portion 24 when viewed along the circumferentialdirection of the inner tube 2. For example, as shown in FIG. 5, thesharply enlarged portion 25A may be arranged upstream of the gentlyenlarged portion 24. This promotes spreading of the exhaust gas G by theenlarged diameter portion 23, thus facilitating rapid and uniformmixture of the exhaust gas G into the atmosphere.

(3b) In the tail pipes of the above-described embodiments, thecommunication holes 4A and 4B do not necessarily have to be arranged inthe sharply enlarged portions 25A and 25B, respectively. For example, asshown in FIG. 6, two or more communication holes 4C may be arranged inthe gently enlarged portion 24. Alternatively, communication holes maybe arranged in both of the gently enlarged portion and the sharplyenlarged portion(s).

(3c) In the tail pipes of the above-described embodiments, the enlargeddiameter portion 23 does not necessarily have to comprise the gentlyenlarged portion 24 and the sharply enlarged portions 25A and 25B. Theenlarged diameter portion 23 may comprise only the gently enlargedportion 24. Furthermore, the inner tube 2 does not necessarily have tocomprise the enlarged diameter portion 23.

(3d) The function(s) performed by a single element in theabove-described embodiments may be performed by two or more elements.The function(s) performed by two or more elements may be performed by asingle element. Part of the configuration of the above-describedembodiments may be omitted. At least part of the configuration of theabove-described embodiments may be added to or replace the configurationof the above-described other embodiments. Any modes encompassed bytechnical ideas specified by claim language are embodiments of thepresent disclosure.

What is claimed is:
 1. A tail pipe comprising: an inner tube comprisinga discharge port configured such that an exhaust gas is dischargedtherefrom; an outer tube arranged so as to form a space between theouter tube and the inner tube by surrounding an outer peripheral surfaceof the inner tube, an upstream end of the outer tube in a flow directionof the exhaust gas being closed; and at least one communication holeallowing communication between an interior of the inner tube and thespace.
 2. The tail pipe according to claim 1, wherein the inner tubecomprises an enlarged diameter portion enlarged in diameter toward thedischarge port.
 3. The tail pipe according to claim 2, wherein theenlarged diameter portion comprises: a gently enlarged portion having afirst taper angle; and a sharply enlarged portion having a second taperangle larger than the first taper angle.
 4. The tail pipe according toclaim 3, wherein the at least one communication hole is arranged in thesharply enlarged portion.
 5. The tail pipe according to claim 1, whereinthe at least one communication hole is shaped such that a width thereofin a circumferential direction of the inner tube changes along the flowdirection of the exhaust gas.
 6. The tail pipe according to claim 1,wherein a downstream end of the outer tube in the flow direction of theexhaust gas is closed.
 7. The tail pipe according to claim 1, wherein adownstream end of the outer tube in the flow direction of the exhaustgas is open so as to allow communication between the space and anoutside of the outer tube.